Dengue fever (DF) is an old disease; the first record of a clinically compatible disease being recorded in a Chinese medical encyclopaedia in 992. As the global shipping industry expanded in the 18th and 19th centuries, port cities grew and became more urbanized, creating ideal conditions for the principal mosquito vector, Aedes aegypti. Both the mosquitoes and the viruses were thus spread to new geographic areas causing major epidemics. Because dispersal was by sailing ship, however, there were long intervals (10–40 years) between epidemics. In the aftermath of World War II, rapid urbanization in Southeast Asia led to increased transmission and hyperendemicity. The first major epidemics of the severe and fatal form of disease, dengue haemorrhagic fever (DHF), occurred in Southeast Asia as a direct result of this changing ecology. In the last 25 years of the 20th century, a dramatic global geographic expansion of epidemic DF/DHF occurred, facilitated by unplanned urbanization in tropical developing countries, modern transportation, lack of effective mosquito control and globalization. As we go into the 21st century, epidemic DF/DHF is one of the most important infectious diseases affecting tropical urban areas. Each year there are an estimated 50–100 million dengue infections, 500 000 cases of DHF that must be hospitalized and 20 000–25 000 deaths, mainly in children. Epidemic DF/DHF has an economic impact on the community of the same order of magnitude as malaria and other important infectious diseases. There are currently no vaccines nor antiviral drugs available for dengue viruses; the only effective way to prevent epidemic DF/DHF is to control the mosquito vector, Aedes aegypti.